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NAME · USAGE · SKY_COORDINATE_SYSTEMS · SEE_ALSO

NAME

ccsystems -- list and describe the supported sky coordinate systems

USAGE

help ccsystems

SKY COORDINATE SYSTEMS

The sky package supports the equatorial ("fk4", "fk4-noe", "fk5", "icrs"), ecliptic, galactic, and supergalactic celestial coordinate systems. In most cases and unless otherwise noted users can input their coordinates in any one of these systems as long as they specify the coordinate system correctly.

Considerable flexibility is permitted in how the coordinate systems are specified, e.g. J2000.0, j2000.0, 2000.0, fk5, fk5 J2000, and fk5 2000.0 all specify the mean place post-IAU 1976 or FK5 system. Missing equinox and epoch fields assume reasonable defaults. In most cases the systems of most interest to users are are "icrs", "j2000", and "b1950" which stand for the ICRS J2000.0, FK5 J2000.0 and FK4 B1950.0 celestial coordinate systems respectively. The full set of options are listed below:

equinox [epoch]
The equatorial mean place post-IAU 1976 (FK5) system if equinox is a Julian epoch, e.g. J2000.0 or 2000.0, or the equatorial mean place pre-IAU 1976 system (FK4) if equinox is a Besselian epoch, e.g. B1950.0 or 1950.0. Julian equinoxes are prefixed by a J or j, Besselian equinoxes by a B or b. Equinoxes without the J / j or B / b prefix are treated as Besselian epochs if they are < 1984.0, Julian epochs if they are >= 1984.0. Epoch is the epoch of the observation and may be a Julian epoch, a Besselian epoch, or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to the epoch type of equinox if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date. If undefined epoch defaults to equinox.
icrs [equinox] [epoch]
The International Celestial Reference System where equinox is a Julian or Besselian epoch e.g. J2000.0 or B1980.0. Equinoxes without the J / j or B / b prefix are treated as Julian epochs. The default value of equinox is J2000.0. Epoch is a Besselian epoch, a Julian epoch, or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Julian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date. If undefined epoch defaults to equinox.
fk[equinox] [epoch]
The equatorial mean place post-IAU 1976 (FK5) system where equinox is a Julian or Besselian epoch e.g. J2000.0 or B1980.0. Equinoxes without the J / j or B / b prefix are treated as Julian epochs. The default value of equinox is J2000.0. Epoch is a Besselian epoch, a Julian epoch, or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Julian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date. If undefined epoch defaults to equinox.
fk[equinox] [epoch]
The equatorial mean place pre-IAU 1976 (FK4) system where equinox is a Besselian or Julian epoch e.g. B1950.0 or J2000.0, and epoch is the Besselian epoch, the Julian epoch, or the Julian date of the observation. Equinoxes without the J / j or B / b prefix are treated as Besselian epochs. The default value of equinox is B1950.0. Epoch is a Besselian epoch, a Julian epoch, or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Besselian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date. If undefined epoch defaults to equinox.
noefk[equinox] [epoch]
The equatorial mean place pre-IAU 1976 (FK4) system but without the E-terms where equinox is a Besselian or Julian epoch e.g. B1950.0 or J2000.0, and epoch is the Besselian epoch, the Julian epoch, or the Julian date of the observation. Equinoxes without the J / j or B / b prefix are treated as Besselian epochs. The default value of equinox is B1950.0. Epoch is a Besselian epoch, a Julian epoch, or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Besselian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian day. If undefined epoch defaults to equinox.
apparent epoch
The equatorial geocentric apparent place post-IAU 1976 system where epoch is the epoch of observation. Epoch is a Besselian epoch, a Julian epoch or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Besselian epochs if the epoch value < 1984.0, Julian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date.
ecliptic epoch
The ecliptic coordinate system where epoch is the epoch of observation. Epoch is a Besselian epoch, a Julian epoch, or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Besselian epochs if the epoch values < 1984.0, Julian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian day.
galactic [epoch]
The IAU 1958 galactic coordinate system. Epoch is a Besselian epoch, a Julian epoch or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Besselian epochs if the epoch value < 1984.0, Julian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date. The default value of epoch is B1950.0.
supergalactic [epoch]
The deVaucouleurs supergalactic coordinate system. Epoch is a Besselian epoch, a Julian epoch or a Julian date. Julian epochs are prefixed by a J or j, Besselian epochs by a B or b. Epochs without the J / j or B / b prefix default to Besselian epochs if the epoch value < 1984.0, Julian epochs if the epoch value <= 3000.0, otherwise epoch is interpreted as a Julian date. The default value of epoch is B1950.0.

Fields enclosed in [] are optional with the defaults as described. The epoch field for the "icrs" , "fk5", "galactic", and "supergalactic" coordinate systems is only used if the input coordinates are in the equatorial fk4, noefk4, fk5, or icrs systems and proper motions are used to transform from coordinate system to another.

SEE ALSO


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